The present invention relates to refractory compositions useful for making injectable pastes having a very low water content.
Refractory pastes are commonly produced by refractory manufacturers, these pastes functioning as repairing pastes intended for injection into various steel-making, petrochemical or other equipment whenever a hot spot appears on a steel wall thereof. These hot spots can result from the partial destruction of the refractory lining or merely from the opening of one or more joints which allows the passage therethrough of hot gases.
This injection technique is commonly practiced, for example, on blast furnaces, cowpers, hot gas ducts, primary or secondary petrochemical furnaces, transfer lines and the like.
Heretofore, the injected refractory pastes were mixtures of clay and chamotte in which were sometimes added a varying amount of refractory cements. For obtaining suitable injectable pastes, i.e. pastes capable of flowing into the cracks or the damaged lining, it was necessary to incorporate in the pastes more than 15% by weight of water, usually more than 25% by weight of water and, in some cases, more 30% by weight of water. These high water contents result in hardened and fired refractory masses or bodies which have porosities higher than 30% and, sometimes, up to 40%.
These known refractory pastes exhibit thus two important drawbacks:
low strength due to the fact that the high water amount in the pastes gives, after drying and possible setting, porous products; PA1 easy creation of additional cracks therein since the sudden release of this high water amount in the paste when the paste is injected into a hot lining tends to create in the injected mass channels which are the source of incipient cracks for new cracks or passages for the hot gases. PA1 (3) 10 to 30%, preferably 15 to 25%, by weight of a very fine fraction comprised of particles at least 50% of which are smaller than 5 microns, the finest particles being not smaller than 0.1 micron; and PA1 (4 )10 to 30%, preferably 15 to 25%, by weight of an ultra fine fraction comprised of particles at least 80% of which are smaller than 0.1 micron, the finest particles being not smaller than 0.01 micron;
In order to overcome these drawbacks, it was often necessary, after a first filling in by injection, to make a second and even a third injection for gradually plugging the native channels in the injected mass.
The present invention has for its object the provision of powdered refractory compositions which require, for the preparation of injectable pastes, only a reduced water proportion, in any case lower than 10% by weight, preferably comprised between 4 and 8% by weight, these pastes undergoing a total shrinkage, after drying and ceramic setting, of lower than 2%, preferably lower than 1%.